scholarly journals The role of sediment supply in the adjustment of channel sinuosity across the Amazon Basin

Geology ◽  
2019 ◽  
Vol 47 (9) ◽  
pp. 807-810 ◽  
Author(s):  
Joshua Ahmed ◽  
José Antonio Constantine ◽  
Thomas Dunne
Keyword(s):  
Amazon Basin ◽  
Sediment Supply ◽  
Landsat Images ◽  
Flow Routing ◽  
Sediment Loads ◽  
Through Flow ◽  
Point Bars ◽  
Meander Bends ◽  
Dominant Direction

Abstract Sediment supplies are a fundamental component of alluvial river systems, but the importance of sustained supplies of externally derived sediments for the evolution of meandering planforms remains unclear. Here we demonstrate the importance of sediment supply in enhancing the growth of point bars that influence the rate of sinuosity increase through flow deflections in meander bends. We use an archive of Landsat images of 16 meandering reaches from across the Amazon Basin to show that rivers transporting larger sediment loads increase their sinuosity more rapidly than those carrying smaller loads. Sediment-rich rivers are dominated by downstream-rotating meanders that increase their sinuosity more rapidly than both extensional and upstream-rotating meanders. Downstream-rotating meanders appear to establish larger point bars that expand throughout the meander, in contrast to extensional meanders, which have smaller bars, and upstream rotating meanders, which are characterized by deposition over the bar head. These observations demonstrate that the size and position of point bars within meander bends influences flow routing and thus controls the dominant direction of meander growth. Rivers with low sediment supplies build smaller point bars, which reduces their capacity to increase meander curvature and the resulting sinuosity.

Synchronization of transport and supply in beach-dune interaction

2009 ◽  
Vol 33 (6) ◽  
pp. 733-746 ◽  
Author(s):  
Chris Houser
Keyword(s):  
Sediment Supply ◽  
Limited Capacity ◽  
Storm Events ◽  
Nearshore Processes ◽  
Transport Studies ◽  
Lack Of Information ◽  
Dynamic Constraint ◽  
Explicit Recognition ◽  
Process Scale

This review considers the role of nearshore processes and morphological change as a flexible and dynamic constraint on the supply and transport of sediment between beach and dune. It is argued that the lack of information in this regard remains a central barrier to the development of a theory of beach-dune interaction that can be translated across scales and between field sites. Existing beach-dune models do not consider how and when sediment gets transferred to the backshore where it becomes available for transport by wind. Rather, existing models largely ascribe regional variations in dune morphology to fixed constraints on beach slope and sediment budget, without explicit recognition of processes involved. Recent (process-scale) transport studies have shown that the transfer of sediment is both spatially variable and temporally intermittent as a result of transport limitations across the beachface. While these studies have identified varied controls on sediment transport and exchange, there remains a limited capacity to predict the evolution of beach-dune systems, largely because the beachface tends to be viewed as a static transport surface without regard to supply or to the changing limits to transport. Following storm erosion, dune recovery first requires that the beach recovers through the onshore migration and welding of nearshore bars, followed by accretion in the backshore to create a supply of sediment for transport by the wind. The dependence of dune recovery on the synchronization of transport events with the recovery of sediment supply in the backshore creates a strong asymmetry in dune recovery that makes barrier island susceptible to widespread erosion and breaching if a change in the frequency or grouping of storm events is capable of resetting the bar system (offshore) before the next extreme storm.

scholarly journals The extreme 2014 flood in south-western Amazon basin: the role of tropical-subtropical South Atlantic SST gradient

2014 ◽  
Vol 9 (12) ◽  
pp. 124007 ◽  
Author(s):  
Jhan Carlo Espinoza ◽  
José Antonio Marengo ◽  
Josyane Ronchail ◽  
Jorge Molina Carpio ◽  
Luís Noriega Flores ◽  
...  
Keyword(s):  
Amazon Basin ◽  
South Atlantic ◽  
Sst Gradient

scholarly journals Atmospheric CO2 budget over the Amazon basin: the role of convective systems

2011 ◽  
Vol 26 (4) ◽  
pp. 529-540
Author(s):  
Valdir Herrmann ◽  
Saulo Ribeiro de Freitas
Keyword(s):  
Amazon Basin ◽  
Transport Model ◽  
Conservation Equation ◽  
Atmospheric Modeling ◽  
Convective Transport ◽  
Atmospheric Co2 ◽  
Moist Convection ◽  
Convective Systems ◽  
Deep Moist Convection

This work studies the atmospheric CO2 budget in the Amazon basin, focusing on the role of shallow and deep convective systems. The vertical redistribution of CO2 is numerically simulated using an Eulerian transport model coupled to the Brazilian developments on the Regional Atmospheric Modeling System (BRAMS). The transport model includes grid-scale advection, diffusion in the PBL (Planetary Boundary Layer) and convective transport by sub-grid shallow and deep moist convection. In the simulation, the mass conservation equation is solved for six tracers, including or not the shallow and deep moist convection terms. The rectifier effect is also showed through simulation of the transport to the free troposphere of PBL air masses with low CO2 concentrations due to assimilation by vegetation during the afternoon, when both CO2 fixation and convection are at their peak. The model is applied to simulate July 2001 with a 30 km grid resolution covering the northwest part of South America. We compare the model results with airborne CO2 observations collected in the Amazon basin during the 2001 CLAIRE field campaign.

scholarly journals PENGARUH PERGERAKAN MEANDER TERHADAP KESEIMBANGAN ALUR SUNGAI

2019 ◽  
Vol 1 (2) ◽  
pp. 45
Author(s):  
Siti Murniningsih
Keyword(s):  
Sediment Load ◽  
Low Impact Development ◽  
Channel Cross Section ◽  
Fluvial System ◽  
Outer Banks ◽  
Meandering River ◽  
Sediment Loads ◽  
Meander Bends ◽  
Minimum Velocity ◽  
Sedimentation Processes

<span><em>Most of the river in Indonesia has a meander area especially located at the lower reach. Since the pattern of </em><span><em>the community behaviour in Indonesia, people live in surrounding or along the river while the river plains </em><span><em>and delta consist of alluvial soils, thus, meander migration usually occurs as a response to natural or manmade disturbances of the fluvial system. Meander River in urban area usually encourage sediment transport </em><span><em>problem such as riverbed aggradations at the area surrounding inside of the bank then will decrease the </em><span><em>river capacity in retaining flood while simultaneously eroding on the outer banks of meander bends. </em><span><em>Regarding velocity distribution at the channel cross section, the minimum velocity is occurring on the inside </em><span><em>of the meander, therefore some of the sediment loads is deposited. Related with the phenomena, protection </em><span><em>against sedimentation and erosion along meandering river extremely needed. Previously, river adjustment </em><span><em>within meander area are continually being made, therefore, eventually the gradient of a stream is altered to </em><span><em>accommodate the volume of water and the velocity necessary to transport the sediment load. In this paper,</em><span><em>understanding of various phenomenon’s in the meander area due to the sedimentation processes are </em><span><em>described and propose the new concept of protection with low impact development (LID) approach.</em></span></span></span></span></span></span></span></span></span></span></span><br /><br class="Apple-interchange-newline" /></span>

scholarly journals Autogenic translation and counter point bar deposition in meandering rivers

2021 ◽  
Author(s):  
Z. Sylvester ◽  
P.R. Durkin ◽  
S.M. Hubbard ◽  
D. Mohrig
Keyword(s):  
Satellite Imagery ◽  
Riparian Vegetation ◽  
Kinematic Model ◽  
Time Lapse ◽  
Sediment Deposition ◽  
Lateral Migration ◽  
Meandering Rivers ◽  
Point Bar ◽  
Point Bars ◽  
Meander Bends

Although it has long been recognized that deposition along meandering rivers is not restricted to convex banks (i.e., point bars), the consensus is that sediment deposition on concave banks of channel bends mostly occurs when meander bends translate downstream because erosion-resistant barriers inhibit their lateral migration. Using a kinematic model of channel meandering and time lapse satellite imagery from the Mamoré River in Bolivia, we show that downstream translation and associated concave bank deposition are essential, autogenic parts of the meandering process, and resulting counter point bars are expected to be present whenever perturbations such as bend cutoffs and channel reoccupations create short bends with high curvatures. The implication is that zones of concave bank deposition with lower topography, finer-grained sediment, slack water, and riparian vegetation that differs from point bars are more common than previously considered.

scholarly journals Lesia Ukrainka and Mykhailo Hrushevskyi: creative connections and sociopolitical views

2021 ◽  
pp. 59-65
Author(s):  
O. Tur ◽  
V. Krot  ◽  
V. Shabunina
Keyword(s):  
Scientific Communication ◽  
Western World ◽  
The Political ◽  
Public Figure ◽  
Historical Method ◽  
One Stage ◽  
Political Views ◽  
The Common ◽  
Dominant Direction

The article is devoted to the study of little-known pages of Ukrainian journalism, in particular, the critical socio-historical and epistolary heritage of Lesya Ukrainka and M. Hrushevsky as iconic figures of Ukrainian culture. It is pointed out that the insufficient study of creative contacts between the writer Lesya Ukrainka and the political and public figure, the historian, the publicist M. Hrushevsky, is caused by ideological factors, which in Soviet times led to the withdrawal of information about the contacts of these figures from scientific communication. It was emphasized that the dominant direction of the "Great Ukrainian" and "Daughter of Prometheus", as evidenced not only by their literary-critical, journalistic works but also their correspondence, was the departure from the traditional Little Russian type of thinking, formation of European spiritual landmarks and values, reflection on Ukrainian "Historical" fate. The use of the historical method revealed the common socio-political views of Lesya Ukrainka and M. Hrushevsky on the role of the Ukrainian intellectuals, the development of Ukrainian culture, the formation of the European vector of development, bridging the gap and returning to a one-stage life with the Western world.

scholarly journals Strategic basin and delta planning increases the resilience of the Mekong Delta under future uncertainty

2021 ◽  
Vol 118 (36) ◽  
pp. e2026127118 ◽  
Author(s):  
R. J. P. Schmitt ◽  
M. Giuliani ◽  
S. Bizzi ◽  
G. M. Kondolf ◽  
G. C. Daily ◽  
...  
Keyword(s):  
Land Subsidence ◽  
Mekong Delta ◽  
Sediment Management ◽  
Sediment Supply ◽  
Sea Levels ◽  
Sediment Yields ◽  
Development Scenarios ◽  
Climate Resilience ◽  
Rising Sea Levels

The climate resilience of river deltas is threatened by rising sea levels, accelerated land subsidence, and reduced sediment supply from contributing river basins. Yet, these uncertain and rapidly changing threats are rarely considered in conjunction. Here we provide an integrated assessment, on basin and delta scales, to identify key planning levers for increasing the climate resilience of the Mekong Delta. We find, first, that 23 to 90% of this unusually productive delta might fall below sea level by 2100, with the large uncertainty driven mainly by future management of groundwater pumping and associated land subsidence. Second, maintaining sediment supply from the basin is crucial under all scenarios for maintaining delta land and enhancing the climate resilience of the system. We then use a bottom-up approach to identify basin development scenarios that are compatible with maintaining sediment supply at current levels. This analysis highlights, third, that strategic placement of hydropower dams will be more important for maintaining sediment supply than either projected increases in sediment yields or improved sediment management at individual dams. Our results demonstrate 1) the need for integrated planning across basin and delta scales, 2) the role of river sediment management as a nature-based solution to increase delta resilience, and 3) global benefits from strategic basin management to maintain resilient deltas, especially under uncertain and changing conditions.

scholarly journals Sedimentation and sediment geochemistry in a tropical mangrove channel meander, Sungai Kerteh, Peninsular Malaysia

2020 ◽  
Author(s):  
Hasrizal Bin Shaari ◽  
Qatrunnada Mohd Nasir ◽  
Che Abd Rahim Mohamed ◽  
Abdul Hafidz Yusoff ◽  
Wan Mohd Afiq Wan Mohd Khalid ◽  
...  
Keyword(s):  
Grain Size ◽  
Sedimentation Rate ◽  
Sediment Cores ◽  
Peninsular Malaysia ◽  
Sediment Supply ◽  
Sediment Geochemistry ◽  
Spatial And Temporal Variability ◽  
Tidal Channels ◽  
Point Bar ◽  
Meander Bends

Abstract Tropical mangrove swamps are commonly characterized by dense networks of tidal channels that may show pronounced meandering and dendritic patterns. Channel meanders are sometimes accompanied by cut offs, and, like classical fluvial meanders, record changes in hydrology and sedimentation over time. Channel meandering can, thus, be an important process that contributes to spatial and temporal variability in the preserved record of the sedimentology and geochemistry of mangrove sediments. The aim of this study is to highlight changes in channel meander sedimentation in response to a meander cut-off in a tropical mangrove swamp. Two short sediment cores were sampled, respectively from a point bar (core KR1, 122 cm) at the junction with the neck cut-off and inside the cut-off (core KR2, 98 cm) in the Sungai Kerteh mangroves of Peninsular Malaysia. The profile comparison was based on sediment characteristics, total organic carbon (TOC) and selected elements (Fe, Na, Mg, Mn, Ba and Sr). Sedimentation rates at both sites were determined from 210Pb. A smaller standard deviation of mean grain size (MGS) was found at the point bar (4.37±0.51 ϕ) than in the cut-off (4.43 ±1.76 ϕ), indicating a difference in flow velocity between the two settings. A small difference in sedimentation rate between the upper (0.41 cm.yr-1) and bottom (0.50 cm.yr-1) parts of core KR1 suggests that water velocity at the point bar area has been rather uniform over the timescale of sedimentation. On the other hand, a higher sedimentation rate in the bottom (0.60 cm.yr-1), compared to the upper (0.39 cm.yr-1) part of core KR2 may reflect a reduction in sediment supply following cut-off. This change also resulted in increased accumulation of selected elements and TOC at the cut-off site from a depth of ~ 60 cm to the core-top segment probably associated with a slowing down of sediment settling. A higher TOC recorded in the cut-off (2.74±1.42%) compared to the point bar (1.14±0.46%) suggests a propensity for prolonged in-situ accumulation of organic matter in the abandoned meander bend. This study provides grain-size and sediment geochemical information that is consistent with patterns of long-term active and inactive sedimentation in the meander bends of mangrove channels.

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